1. Field of the Invention
This invention relates to the processing of tires for uniformity correction and, more particularly, to a method and apparatus for testing tires for force variations more rapidly than previously possible and for grinding the tested tires to eliminate such force variations.
2. Description of the Prior Art
In the art of manufacturing pneumatic tires, various components such as belts, beads, liners, treads, plies of rubberized cords, and the like are segmentally assembled. During the assembling, structural nonuniformities may occur. When nonuniformities are of sufficient magnitude, they will cause force variations on a surface, such as a road, against which the tires roll and thereby produce vibrational and accoustical disturbances in the vehicle upon which the tires are mounted.
Force variations in rotating tires may occur in either the radial or lateral direction. Force variations are anomalies which result from "hard" and/or "soft" spots in the tires caused by structural nonuniformities such as inconsistent wall thickness, ply turn-up variations, bead set, ply arrangement and other deviations. Regardless of the cause of the force variations, when such variations exceed the acceptable miniumum level, the ride of a vehicle utilizing such tires will be adversely affected.
Excessive force variations may be eliminated or reduced to an acceptable level by processing on a tire uniformity machine. Typical examples of known tire uniformity machines are described, for example, in U.S. Pat. Nos. 3,574,973 to Rader; 3,725,163 to Hofert; and 4,458,451 to Rogers et al. Where the force variations are detected, correction is effected by removing selected portions of tread rubber with a pair of grinders, one located in association with each shoulder of the tire. Removal of rubber in a proper amount and at the proper locations effects a reduction in force variations to an acceptable level for improving the ride of the vehicle upon which such tires are mounted.
In typical tire uniformity machines, a tire is mounted on a rotatable axle, inflated and then rotated against a loadwheel for a testing phase. During its initial revolutions, the tire is loaded at a first predetermined load. Thereafter, the tire is rotated under full load for additional revolutions. These revolutions, generally referred to as "warmup" time, are performed to relieve any "set" in the tire that may have occurred during storage. Detection for excessive force variations is started after the warmup is completed.
Force variations are transmitted from the tire to the loadwheel where such force variations are sensed by transducers, such as load cells. Electrical signals representing the magnitude of the measured force variations are generated and sent to a microprocessor. The measurement of force variations is generally performed during one to three revolutions of the tire depending on the design of the electrical circuitry employed. The signals are processed and compared to predetermined upper and lower limits of correctable force variations. In response to the signals, the computer makes a grind or no-grind decision by comparing the actual measured force variations to the upper and lower limits. If the measured force variations do not exceed the lower limit, no grinding is performed, the tire is graded as acceptable, and it is removed from the machine. If the measured force variations exceed the upper limit, the force variations are considered noncorrectable, no grinding is performed and the tire is also removed from the machine.
If the measured force variations are between the upper and lower limits, grind instruction signals are generated and the grinding phase is initiated. Mechanisms are actuated by the grind instruction signals to move rotary grinders to the shoulders of the tire. The grinders remove selected quantities of rubber from selected areas of the shoulders for reducing the force variations to an acceptable level at or below the lower limit. The time required to reduce the force variations in a tire to an acceptable level is dependent upon the amount of rubber to be removed and the rotational speed of the tire during processing.
Tire uniformity machines may be rendered more efficient by several techniques. First, the radial component of the force variations may be detected more efficiently or more accurately. U.S. Pat. Nos. 3,754,358 to Schively et al and 4,458,451 to Rogers, for example, are related to tire uniformity machines with improvements for radial correction. Second, the lateral component of the force variations may be detected more efficiently or more accurately. U.S. Pat. Nos. 4,095,374 to Ugo and 4,112,630 to Brown, for example, are related to tire uniformity machines with improvements for lateral correction. Third, the rotational speed of the tire on the uniformity machine may be increased. While grinding may be done at one of a plurality of slower speeds, speeds below the testing speed, testing is typically done at a constant speed of 60 revolutions per minute (rpm), the industry standard. Note U.S. Pat. Nos. 3,500,681 to Shively and 3,574,973 to Rader. It might be considered that increasing the rotational speed of a tire on a uniformity machine might be accomplished simply as by an increase in a mechanical gearing ratio or the like. Such is not the case since the mechanically increased speed must be compatible with the circuitry and mechanisms for both sensing and grinding. No prior art patent or known commercial device teaches or suggests the operating of tire uniformity machines at increased speeds while retaining high accuracy and efficiency.
As illustrated by the great number of prior patents and commercial devices, efforts are continuously being made in an attempt to more efficiently correct tire nonuniformity. None of these prior art efforts, however, suggests the present inventive combination of method steps and component elements arranged and configured for correcting tire uniformity at increased speeds and maintained accuracy as disclosed and claimed herein. Prior methods and apparatus do not provide the benefits of the present invention, which achieves its intended purposes, objectives and advantages over the prior art devices through a new, useful and unobvious combination of method steps and component elements, through no increase in the number of functioning parts, at a reduction in operational cost, and through the utilization of only readily available materials and conventional components.
These objects and advantages should be construed as merely illustrative of some of the more prominent features and applications of the present invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and advantages as well as a fuller understanding of the invention may be had by referring to the summary and detailed description of the preferred embodiment of the invention in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.